The invention relates to an imaging system and a method for loading a printing plate. Traditionally, a prepress process requires the development of a negative or positive film of data to be printed. The film is subsequently copied onto a printing plate. Then, the printing plate is employed for offset printing activities. The computer-to-plate imaging process comprises a digital technology transferring text and/or images directly onto the printing plate by means of an radiation exposure unit. Thereby the intermediate film production is bypassed.
A known imaging system for performing a computer-to-plate imaging process on printing plates comprises a plate imaging bed for exposing radiation to a printing plate, the bed being provided with an input section for receiving a printing plate and an output section for transferring the printing plate to a chemical processing unit. In operation, a loading device loads a printing plate from a multiple plate stack to the input section of the plate imaging bed.
Such an imaging system is known. The printing plate comprises a support substrate that can be metal or polymer based. Popular metal supports are aluminum based. Other metal supports comprise copper and/or steel, but polymer supports as used in flexography and polyester based plates are also possible. On this substrate, a radiation sensitive coating is provided which can easily be damaged during handling. In an initial stage, the printing plate is stacked together with a multiple set of printing plates on a multiple plate stack. During the process, individual printing plates are loaded from the stack towards the input section of the plate imaging bed by means of the loading device. Subsequently, the printing plate is locally sensitized by radiation that is exposed by the imaging system and transported to the end section of the printing plate. Then, the printing plate is transferred to art optional external conveyor system or a chemical processing unit, for plate types that require chemical processing. The conveyor or chemical processing unit is positioned adjacent the output section of the imaging bed for optional further processing.
The multiple plate stack is supported by a supporting unit, such as a cassette. In a conventional imaging system, the height of the cassette is adjustable, so that the height of the upper plate of the stack can be kept at a desired level, thus facilitating the transfer of an upper printing plate from the stack to the imaging bed without being damaged. Further, the lower level of the stack is fixed while the loading device is movable in the vertical direction, so that an upper printing plate can be lifted from the stack and can be brought to a desired level corresponding to the height of the imaging bed.
A disadvantage of such a loading mechanism is its complexity, causing time loss and/or increased costs. Further, the known loading mechanism is in general only suitable for handling printing plates in a specific configuration of imaging bed and stack structure.
In practice, two or more plate stacks can be positioned near the input section of the imaging bed. A further disadvantage is, that this further increases the complexity of the height adjusting mechanisms.
Comparable handling systems are known from patent publication EP 1 473 153, wherein a flexographic plate is exposed to e.g. ultra violet light.